There is only one file type that uses the .MPROJ extension:
Project file created by Mine-imator, a Minecraft animation creation program; contains items, mobs (players), and terrain for the scene; includes an animation timeline, project description, and screen resolution; can be exported to an .AVI video when complete.
Mine-imator can be used for making Minecraft movies published to YouTube and other video sharing websites.
NOTE: MPROJ files replace .MANI files in version 1.0 of Mine-imator.
Updated: July 17, 2014